1. Field of the Invention
This invention relates to an engine output characteristic control system for a vehicle which controls the output characteristic versus the accelerator depression of an engine of the vehicle.
2. Description of the Prior Art
There has been proposed an electric throttle system in which the throttle valve is mechanically disconnected from the accelerator pedal and is electrically driven by an actuator such as an electric motor in response to depression of the accelerator pedal. In such an electric throttle system, the driver can select a power mode which emphasizes running performance or an economy mode which emphasizes fuel economy.
In accordance with a general control, when the power mode is selected, the gear-shift lines for the automatic transmission are shifted toward the higher vehicle speed side so that a lower gear speed is used and at the same time the throttle opening gain for a given accelerator depression (amount of depression of the accelerator pedal) is increased, while when the economy mode is selected, the gear-shift lines for the automatic transmission are shifted toward the lower vehicle speed side so that a higher gear speed is used and at the same time the throttle opening gain for a given accelerator depression is reduced.
In accordance with an equi-power line control which is effected on the basis of the fuel efficiency for equi-power lines, when the power mode is selected, the gear-shift lines are shifted toward the higher vehicle speed side so that a lower gear speed is used and at the same time the throttle opening gain for a given accelerator depression is reduced, thereby improving the engine response without changing the power, while when the economy mode is selected, the gear-shift lines are shifted toward the lower vehicle speed side so that a higher gear speed is used and at the same time the throttle opening gain for a given accelerator depression is increased, thereby using a lower engine speed range without changing the power so that the fuel efficiency is improved.
In the throttle control system disclosed in Japanese Unexamined Patent Publication No. 63(1988)-25347, the throttle valve is controlled so that the fuel consumption is minimized when the accelerator depression is smaller than a preset value, thereby improving the fuel economy while, when the accelerator depression is not smaller than the preset value, the throttle valve is controlled to correspond to the accelerator depression, thereby improving the running performance.
However the gear-shift maps for the power mode and the economy mode are conventionally set to conform to the greatest common factors of the needs of users and the traffic at the time the vehicle is developed, and accordingly they cannot give an optimal fuel consumption depending on the driver's habit in driving the vehicle and/or the traffic.
For example, when the throttle gain has been set to give an optimal fuel consumption at a certain traffic, the fuel economy will deteriorate at a lower speed traffic since the accelerator is frequently returned and the throttle opening fluctuates frequently due to excessive acceleration of the vehicle. Further at a higher speed traffic, the fuel economy will deteriorate due to excessive depression of the accelerator pedal.